Method of treating cotton for fire retardation

ABSTRACT

THE METHOD DISCLOSED COMPRISES THE STEPS OF FIRST EXPOSING THE INDIVIDUAL PORES OR FIBERS OF A MATERIAL AS MUCH AS POSSIBLE, THEN DISPERSING A DESIRED HYGROSCOPIC POWDER, E.G., UREA-DIAMMONIUM PHOSPHATE WITH A FREE-FLOWING, ANTI-CAKING AGENT SUCH AS PRECIPITATED SILICA, INTO THOROUGH CONTACT WITH THE EXPOSED FIBERS, HUMIDFYING THE EXPOSED FIBERS TO DISSOLVE THE POWDER AND PENETRATE THE FIBERS, E.G., BY A FOG OBTAINED BY MIXING STEAM WITH SATURATED AMBIENT AIR, AND FINALLY DRYING AND/OR CURING THE PENETRATED FIBERS TO GIVE RISE TO THE DESIRED CHARACTERISTIC IMPARTED BY THE PENETRATING SOLUTION SUCH AS FIRE RETARDATION. THE HYGROSCOPIC POWDER IS PREPARED BY DRYING THE CONSTITUENTS PRIOR TO PULVERIZING TO REDUCE THE MOSITURE CONTENT THEREOF TO LESS THAN TEN PERCENT, CIRCULATING HOT AIR DURING THE PULVERIZING PROCESS, AND ADDING A FREE-FLOWING, ANTI-CAKING AGENT BEFORE OR AFTER THE PULVERIZING PROCESS.

United States Patent 3,666,544 METHOD OF TREATING COTTON FOR FIRERETARDATION William L. Kuechler, Jenkintown, Pa., assignor to Proctor &Schwartz, Inc., Philadelphia, Pa. No Drawing. Filed Mar. 12, 1970, Ser.No. 19,107 Int. Cl. (109k 3/28 US. Cl. 117-137 5 Claims ABSTRACT OF THEDISCLOSURE The method disclosed comprises the steps of first exposingthe individual pores or fibers of a material as much as possible, thendispersing a desired hygroscopic powder, e.-g., urea-diammoniumphosphate with a free-flowing, anti-caking agent such as precipitatedsilica, into thorough contact with the exposed fibers, humidifying theexposed fibers to dissolve the powder and penetrate the fibers, e.g., bya fog obtained by mixing steam with saturated ambient air, and finallydrying and/ or curing the penetrated fibers to give rise to the desiredcharacteristic imparted by the penetrating solution such as fireretardation. The hygroscopic powder is prepared by drying theconstituents prior to pulverizing to reduce the moisture content thereofto less than ten percent, circulating hot air during the pulverizingprocess, and adding a free-flowing, anti-caking agent before or afterthe pulverizing process.

BACKGROUND OF THE INVENTION (1) Field of the invention This inventionrelates to the field of hygroscopic chemicals and, more particularly,their preparation and use as a powder in imparting desiredcharacteristics to porous materials.

(2) Description of the prior art Powder compositions such as vinylchloride resin powder have been applied as a chemical agent (binder) tocellulosic and flammable fibers. These powder compositions, such as thevinyl chloride resin powder, have had fire retardant characteristics andhave superficially imparted such to the fibers to which they have beenapplied. Aside from their teaching of powder technology as applied toporous, e.g., fibrous, materials with the inherent fire retardantcharacteristic of some, these compositions do not relate to the presentinvention.

Chemical treatments of porous, e.g., fibrous, materials to thoroughlyimpart characteristics thereto have been accomplished in the pastprincipally by wet processes, i.e., chemicals in water solution. Thesetreatments have resulted in the matting together of the fibers into acompressed, wet batt which has been difiicult and costly to dry andwhich, in the textile field, has compacted the fibers so much thatsubsequent carding has been difficult. The latter problems have beeneliminated to some extent in the textile field by the use of chemicalswhich have been dusted onto the fibers in dry, finely powdered form. Theapplication of such powdered chemicals, such as resins et cetera hasbeen done convevniently at the dofi'er comb of carding type equipmentwhere the fiber is opened (exposed) and agitated and the powderedchemical is dusted onto the exposed fibers to reaily coat and adherethereto. The principles of dust adhesion to fiber surfaces has becomewell-known and established through the development of pad-type dustfilters for air cleaning. Once the powdered chemicals have been dustedonto the exposed fibers, applications of heat and/ or solvent arerequired to soften or melt the powdered chemicals causing the chemicalsto securely coat and adhere to the surfaces of the fibers.

3,666,544 Patented May 30, 1972 However, in many cases such as impartingfire retardant characteristics to the exposed fibers, merely coating oradhering the powdered chemicals to the exposed fibers is not enough. Itis requisite in such cases to dissolve the powdered chemicalssufficiently to allow penetration of the solution into the fibersbecause, obviously, by merely coating the fibers the chemicals could bescrubbed or worn away exposing fibers lacking the desiredcharacteristic.

As stated preiovsuly, chemical penetration of fibers has beenaccomplished by wet processes. These processes have permittedpenetration of the fibers by the solution to give rise to the desiredcharacteristic such as fire retardation. However, as also statedpreviously, the wet processes have had many disadvantages. Althoughsteaming and spraying moisture onto powdered chemicals have beenattempted to obtain desired chemical penetration of the exposed fibers,it should be noted that steaming as implied by the term requires certainsealed, closed environment equipment requirements forvapor-liquid-thermal equilibrium, which in themselves make suchoperations unsatisfactory and spraying results in insufficient moisturecontact because of the large droplet size needed for solution but thesmall droplet size needed for proper flow within the clump or web offibers.

Because of the many disadvantages of the prior art with respect toobtaining desirable penetration of exposed fibers through theapplication of powdered chemicals or wet processes, the invention as setforth hereinafter provides a new powder technology approach forimparting desired chemical characteristics to fibers where chemicalpenetration of the fibers is required.

SUMMARY OF THE INVENTION This invention is directed toward a method ofpreparing a hygroscopic powder and the use of such powder to impartcertain characteristics to porous material.

As an example of the present invention, fire retardation of cottonfibres is accomplished by the application of a urea-diammoniumphosphate-precipitated silica composition in powder form to opened,individualized cotton fibers with subsequent humidification, heatingand/or curing of the resultant fiber. The powder composition is obtainedby drying the constituents prior to pulverizing and then pulverizingunder hot air circulation with the addition before or after of afree-flowing, anti-caking agent such as the precipitated silica. Otherhygroscopic powders may be formed including combinations of ammoniumchloride and ammonium sulfate, or ammonium sulfamate, each, of course,with a free-flowing, anti-caking agent such as precipitated silica.

It is therefore an object of the present invention to arrive at aneiiective ethod of chemically treating porous material. This and otherobjects, features and advantages of the present invention will becomemore apparent when reading the following description and claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT The prior art has establishedpowder technology and its application to porous, e.g., fibrous, materialby steam or spray dispersion. The use of steam permitted fiberpenetration by the dissolved powders but required sealed environmentsmaintaining a vapor-liquid-thermal equilibrium. The use of spraydispersions merely effected penetration of the surface fibers of a clumpof fibers or a web but, because of the relatively large droplets whichcould not reach the interior fibers, provided an uneven distribution ofthe moisture to the powder with a resultant lack of the desiredcharacteristics in the interior fibers. The alternative, of course, hasbeen the wet processes which, although permitting penetration of thedesired solutions throughout the fibers, resulted in substantial dryingand processing problems.

The need, therefore, has existed for an improvement in powder technologywhich would eliminate the partial penetration resulting from spraydispersion techniques and the sealed environment requirement of steamtechniques.

This need has been satisfied by the present invention which advancespowder technology to permit utilization of powdered hygroscopiccompositions in combination with a moisturizing technique requiring anenvironment for the exposed pores or fibers of ambient, saturated air inconjunction with a steam source. The ambient and steam interactionproduces a condensation of extremely fine (low micron to sub-micron)droplets which reach substantially all of the individual pores or fibersof a clump of fibers or a web and enable penetration of the resultingpowder-droplet solution into the individual fibers or throughout theweb. Of course, this penetration of the present invention would notarise if the powder were not of a hygroscopic nature to permit its readydissolution by the fine droplets of relatively low temperature.

Since the constituents of a hygroscopic powder are likely each inthemselves to be of a hygroscopic nature, the problems of preparation ofsuch a powder are acute because of the high, mutual solubility of suchconstituents in aqueous soltuion. Thus, an ambient environment will leadto absorption of moisture from the air and lead to the dissolving of theconstituents to negate any powdered end result. In order to counteractthe hygroscopic nature of the constituents or any one of them, it hasbeen found that the drying of the constituents prior to pulverizing toreduce the water content thereof to less than about ten percent with theaddition of about one-half to five percent by weight of a free-flowing,anti-caking agent before the pulverizing step, and then pulverizing theconstituents into the desired powder under the circulation of hot air ata temperature of between about 150 to 250 F. results in a hygroscopicpowder which may be dispersed onto exposed fibers and yet remain stableunder contemplated ambient conditions until further activated by asubsequent humidifying step. As a modification of this hygroscopicpowder preparation, it has also been found that the free-flowing agentmay be added subsequent to the pulverizing process but this does notassure stability during pulverizing to the extent that the additionprior to the pulverizing does. Also, of course, by adding thefree-flowing agent prior to pulverizing', the necessary particle size ofthe powder is assured to be more uniform.

With respect to the application of the powder to porous, e.g., fibrousmaterial, it should be noted that complete opening and exposure of thepores (fibers) to the powder is desirable to accomplish proper results.Any conventional technique of opening the fibers prior to the dispersionof the powder is acceptable as long as the dispersion can in fact reachthe individual pores (fibers) throughout the clump of fibers or web andadhere thereto.

Once the hygroscopic powder has been properly dispersed throughout theopened and exposed fibers, the steps of dissolution by humidificationand drying and/or curing are initiated. Humidification is obtained byexpos-' ing the powder-fiber mixture to a fog which is caused by theintroduction of steam to an ambient closed environment. Because of thetemperature dilferential between the ambient and the steam, extremelyfine droplets of moisture will condense from the stream. These dropletsof low micron to sub-micron size, because of their minute size, contactthe individual fibers throughout the clump or web and readily dissolvethe hygroscopic powder adhering to the fibers with the resultantsolutions penetrating the fibers thoroughly. The penetrated fibers arethen dried under conventional principles and cured, if necessary, toarrive at the desired characteristic or characteristics imparted by thehygroscopic powder. Because of the penetration of the fiber by thesolution imparting these characteristics, the fibers retain thecharacteristic throughout and are not susceptible to the loss thereofthrough succeeding process operations of wear. It should be noted thatgenerally, because of the penetration and absorption of the solution bythe fibers, the fibers increase significantly in volume to possiblyofiset at least part of the entire process cost because of the increasedbulk directly resulting therefrom.

With the present invention stated above in general, we now refer to aspecific example. Industry requirements as well as governmentregulations have tended toward fire retardant cotton batting. Thisbatting typically consists of a blend of seventy percent of first cutlinters and thirty percent of cotton wastes. A typical batting producionline includes bale breakers, a blending conveyor, a picker and a Willowfrom where the blend of linters and waste is fed to three or fourgarnetts and their corresponding lappers.

Chemical treatment of cotton batting in the past has been doneprincipally by saturation processes and processes of the cotton flotetype, with the same disadvanrtages of the wet processes previouslydiscussed. The present application of fire retardant characteristics tocotton fibers to be used in batting or otherwise includes the use ofurea (66% by weight) and diammonium phosphate (33% by weight) of knownfire retardant capability in powder form to the opened fibers of cotton.The powder form includes a free-flowing, anti-caking agent, preferablyprecipitated silica (1% by weight). The latter agent assists inpreventing dissolution of the urea and diammonium phosphate inthemselves because of their known hygroscopic nature.

The hygroscopic powder having the above-mentioned constituents isprepared by first drying the urea and diammonium phosphate stock priorto pulverizing to reduce the moisture content thereof to less than tenpercent and preferably in the order of five percent, then adding thefree-flowing agent of precipitated silica in the order of one percentalthough a range of from about one-half to five percent may beconsidered. This mixture is then pulverized under the circulation of hotair in the temperature range of between about 150 to 250 F. butpreferably around 225 F. to arrive at a uniform particle size of between50 to 150 microns in diameter and pref erably in the order of microns.The free-flowing agent may be added as most recently stated but may beadded subsequent to the pulverizing step in which case the agent shouldalready be formed to the uniform particle size. The resultant powder isdesirably maintained at room temperature in an environment suflicientlydry to preclude the dissolution of the powder by means of moisturereadily absorbed from the environment.

The application of the hygroscopic powder to the fibers is preceded bythe opening of the fibers as much as pos-" sible to obtain an adequateindividual fiber exposure to adherence of the powder once dispersed intothe fiber stock. To obtain the needed exposure and individualization ofthe fiber stock, the cotton fiber may be processed on a conventionalshredder of the type sold by :Proctor & Schwartz, Inc. having Model No.170. This shredder should preferably be modified to replace thevibrating comb with a rotary wire roll to result in an individualizedfiber take-0E instead of a web-like one. The roll, preferably of rigidV-wire, is utilized to obtain desired powder-exposed fiber contact byintroducing the hygroscopic powder to the fibers before the take-ofi?from the dolfer (where the doffer carries the porous, e.g., fibrous,material on its top) and by substantially reducing powder fly. With thepowder introduced to the fiber processing system at the shredder asmodified so that it initially contacts the fibers prior to take-off,thefinal contact of the powder with the individually exposed fibers fromthe shredder is very substantial. This substantial contact now permitsthe effective utilization of the hygroscopic nature of the powder toobtain thorough penetration of the fibers with which the powder is inadhering, coating contact.

Penetration of the fibers by the hygroscopic powder is obtainedsubsequent to their take-ofi from the doifer of the shredder by exposingthe fibers which have now been superficially coated with the powder to ahumidified atmosphere. Moisture is presented to the opened fibers coatedwith the powder in a closed (but not necessarily sealed) environmentthroughthe introduction of steam to a saturated ambient at a significanttemperature differential. The temperature differential causes acondensation of droplets of moisture (low micron to sub-micron size)which, because of their size, are to flow within the clump of fibers (ora web if such is the application) to be absorbed by the hygroscopicpowders, dissolve same and, as a solution therewith, penetrate thefibers to impart thereto its fire retardant characteristic. The ambientis at a temperature of about 125-200 F. and preferably at about 150 F.,with about five to ten pounds and preferably about seven pounds of theresulting fog per pound of fiber needed to obtain the desired result.

Once the solution of powder in water penetrates the fibers throughout,the fibers are run through conventional drying aparatus preferably ofthe conveyor type. This drying step is carried out in an air temperaturerange of between 150 to 250 F. to reduce the moisture content belowabout ten percent.

Depending on the constituents of the powder, the fibers may be curedsubsequent to drying in any of a number of conventional apparatus. Inany event, it should be noted that the porous, e.g., fibrous, materialsubsequent to drying will be substantially increased in volume becauseof the penetration, drying and/ or curing of the solution of powder andwater therein and will thus result in an additional benefit, possiblyotfsetting part of the process cost by the increased volume.

Although the terms pore and fiber and their derivatives are usedinterchangeably herein, the term pore is intended to be generic to theterm fiber and, thus, is intended to encompass non-fibrous but porousmaterials such as concrete.

Since the preferred embodiment may be modified in numerous ways withinthe scope of the present invention as is shown by the example above, thepreferred embodiment should be viewed as illustrative and not in alimiting sense.

What I claim is:

1. A method of treating cotton for fire retardation comprising the stepsof exposing the pores of said cotton, dispersing a hygroscopic powder onsaid cotton, mixing said .cotton and powder to increase the contacttherebetween about said pores, moisturizing the powder-cotton mixture sothat a solution of the powder is formed which penetrates said pores andreducing the moisture content of said cotton to less than ten percent byweight.

2. The method set forth in claim 1 wherein said hygroscopic powder is amixture of urea-diammonium phosphate-precipitated silica.

3. The method set forth in claim 1 wherein the step of moisturizingcomprises introducing steam to the ambient surrounding saidpowder-cotton mixture.

4. A method of treating cotton for fire retardation with a powder formedfrom at least one hygroscopic stock constituent comprising the steps ofreducing the moisture content of said at least one constituent, adding afree-flowing constituent, pulverizing said constituents while exposingsaid constituents to a controlled environment, exposing the pores ofsaid cotton, dispersing said hygroscopic powder on said cotton, mixingsaid cotton and powder to increase the contact therebetween about saidpores, moisturizing the powder-cotton mixture so that a solution of thepowder is formed which penetrates said pores and reducing the moisturecontent of said cotton to less than ten percent by weight.

5. A method of treating cotton for fire retardation with a powder formedfrom at least one hygroscopic stock constituent comprising the steps ofreducing the moisture content of said at least one constituent,pulverizing said at least one constituent while exposing said at leastone constituent to a controlled environment, adding a free-flowingconstituent, exposing the pores of said cotton, dispersing saidhygroscopic powder on said cotton, mixing said cotton and powder toincrease the contact therebetween about said pores, moisturizing thepowder-cotton mixture so that a solution of the powder is formed whichpenetrates said pores and reducing the moisture content of said cottonto less than ten percent by weight.

References Cited UNITED STATES PATENTS 1,372,860 3/1921 Bennett 117-21758,243 4/ 1904 Goldman 117-21 2,415,112 2/1947 Seymour et al 117-1372,815,761 12/1957 Shearer 117-16 3,027,267 3/1962 Alleman et a1. 117-163,484,372 12/1969 Birchall 106-15 FP 3,172,852 3/1965 Lobos 252-81FOREIGN PATENTS 986,475 3/1965 Great Britain 117-16 WILLIAM D. MARTIN,Primary Examiner -R. M. SPEER, Assistant Examiner U.S. Cl. X.R.

